Study Objective: Many venous access devices (VADs) are routinely flushed with small doses of heparinized saline (2-3 cc, 100 units/cc). In larger intravenous doses, heparin causes immune-mediated thrombocytopenia in 1-3% of patients and leads to heparin-related antibodies in approximately 5-50% of patients. The risk of heparin-induced thrombocytopenia from daily VAD flushing, as reflected in the appearance of heparin-related antibodies, is not known. The purpose of this study is to estimate this risk by testing for heparin-induced antibodies in serum samples. Methods: Presence of heparin-induced antibodies will be evaluated in 120 subjects before VAD insertion and approximately 4 and 8 weeks later. Summary of Findings: To date, 13 subjects have been enrolled.